Remote control system for hydraulic cranes

ABSTRACT

A hydraulic crane, especially when used for loading ships or for other uses where a fixed crane operator could not see the load being picked up or deposited, is controlled with finesse by an operator connected to the control center by a light hydraulic cable. The operator carries a chest unit with the necessary levers, each operating a piston in a master cylinder. The master cylinder is connected through slim lines in the cable to a slave cylinder of identical nature except that its piston-coupled lever is not a handle but operates a main hydraulic control valve at the crane control center. Thus the operator&#39;&#39;s hand movement, however gradual, is exactly reflected by movement of the spool of the control valve. The ports on opposite sides of the piston of the master cylinder are connected to the two ports on the opposite sides of the slave cylinder to form, in effect, a closed circuit. A reservoir for each such circuit has a screwed-in piston to maintain a static pressure substantially eliminating hydraulic backlash. It may be used in initially filling the lines to exclusion of all air.

United States Patent [72] Inventor Wilburn Kelly Brown Morton Grove, Ill. [21 1 Appl. No 687.374 [22] Filed Dec. 1, 1967 [45] Patented Feb. 2, 1971 [73] Assignee' Circle Tool & Mfg. Co.

Des Plaines, ill.

a corporation of Illinois [54] REMOTE CONTROL SYSTEM FOR HYDRAULIC [56] References Cited 1 UNITED STATES PATENTS 2,397,270 3/1946 Kelly 60/54.5 2,965,244 12/1960 Schat 212/68 3,154,199 10/1964 Balogh 212/35 2,720,327 10/1955 Bain 2,924,943 2/1960 Dickinson Primary Examiner-Harvey C. Homsby Attorney-Darbo, Robertson & Vandenburgh trolled with finesse'by an operator connected to the control center by a light hydraulic cable. The operator carries a chest unit with the necessary levers, each operating a piston in a master cylinder. The master cylinder is connected through slim lines in the cable to a slave cylinder of identical nature except that its piston-coupled lever is not a handle but operates a main hydraulic control valve at the crane control center. Thus the operator's hand movement, however gradual, is exactly reflected by movement of the spool of the control valve liThe ports on opposite sides of the piston of the master cylinder are connected to the two ports on the opposite sides of the slave cylinder to form, in efiect, a closed circuit. A reservoir for each such circuit has a screwed-in piston to maintain a static pressure substantially eliminating hydraulic backlash. It may be used in initially filling the lines to exclusion of all air.

PATENIEU FEB 2:971 3559-817 SHEET '4 OF 5 VALVE PATENIEB FEB 2 IIII sum s ar 5 am 1 mm p REMOTE CONTROL SYSTEM FOR HYDRAULIC CRANES INTRODUCTION The invention of which the present disclosure is offered for public dissemination if adequate patent protection is available relates to the remote control of hydraulic cranes. Particularly, it relates to a hydraulically coupled remote control which enables the operator to stand where he can see the load or move to different points to see the load picked up in one point and deposited in another. In either position, or while walking, he can operate the hydraulic control valves with the same finesse as if he were operating them by the usual levers mechanically coupled to the control valves.

An example of a place of great utility for the present invention is, incidentally, a location of its first use, for loading ships. Heretofore, the common method of loading ships has been by deck cranes which included not only relatively long booms but also a relatively high crane mast from which the boom was adjusted by a cable. The operator was located adjacent the tuming axis of the crane and was dependent upon hand signals. One signaler might be at the rail of the ship where he could see the dock site. Another could be at the edge of the hatch so as to see the activity down in the hold, both locations being out of sight to the crane operator.

The present invention encourages the substitution of a hydraulic crane for the mast-type cable crane. This makes the crane more compact, lowers the ship's center of gravity, and lends. itself to complete control by an operator who can walk about while coupled to the control center of the crane by a light hydraulic cable. His ability to be at the edge of the hatch while the activity is in the hold, and at the rail while the activity is on the dock, enables him to dispense with the man or men in these locations. It does better than that, however, since the crane operator can now see exactly what needs to be done instead of relying on signals which are necessarily slower and less exact than knowledge obtained by direct vision. As a result, the overall task of loading or unloading a ship can be quite substantially speeded up.

Hydraulic cranes have long been known in other uses, notably mobile cranes, and their advantages in ordinary locations are well known. Operation is so easy that operators can be quickly trained, and the controls can be actuated with such finesse as to operate at fairly high speed where safe, and nevertheless deposit a load quite gently wherever required. According to the present invention, these advantages are made available for such use as on shipboard, and at the same time, the greater advantages of portable control without loss of other hydraulic crane advantages is achieved.

The invention is also of great utility whenever either of the positions of the pickup or deposit would be out of sight of the crane operator, provided that the operator, with his hydraulically coupled remote control unit, can find a location suitable for viewing both positions.

Additional objects and advantages of the invention will be apparent from the following description and from the drawings.

DESIGNATION OF FIGURES FIG. 1 is a view representing the deck of a ship beside a dock, the full lines showing the crane working with a load in the hold which is viewed by the crane operator at the edge of the hatch, and dotted lines showing the crane extending over the dock where the operation at dock level can be viewed by the crane operator, now moved to a point beside the rail of the ship;

FIG. 2 represents a load being moved up or down within a hold with a crane operator having full view thereof;

FIG. 3 is a side view of a typical hydraulic telescopic-boom crane with the remote control system of the present invention applied to it;

FIG. 4 is an end view of the slave assembly of the hydraulic system, supported by shelf-forming brackets from which it may be removed for inside-ship protection from the elements when not in use;

FIG. 5 is a view that is partially diagrammatic but which includes side views of the master and slave cylinders and pressured reservoir;

FIG. 6 is a longitudinal sectional view through the master cylinder unit and through the pressured reservoir.

INTENT CLAUSE Although the following disclosure offered for public dissemination is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose, as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

GENERAL DESCRIPTION OF HYDRAULIC CRANE AND ITS USE FIG. I represents a ship 11 moored at a dock I2 and provided with two hydraulic cranes I3 and 14. These cranes would naturally be identical.

Preferably, each crane is largely conventional, except for being mounted on shipboard and having features described below.

As seen in FIG. 3, each crane may be supported by a suitable pedestal I6 having a turntable I7 at its top which permits the crane to swing as seen in FIG. 1. Such cranes with unlimited swinging are common, but in the present instance it may be preferred to limit the swinging to protect any upstanding equipment located generally between the two cranes or rearwardly thereof. The crane can be swung hydraulically as by a hydraulic motor 18 controlled for rotation in either direction by one of four or more main crane control valves. A swinging base 19 is carried by the turntable and has pivoted thereto a main boom section 21 sometimes ,called the shipper." A telescopic boom section 22 may be hydraulically extended from and retracted into the main boom section 21, and there may, if desired, be still further telescopic sections for still greater length.

Hydraulic cylinders 23 can be actuated to raise the boom 21, 22 about its pivotal point 24, a counterweight 26 commonly being provided to aid this action especially if a heavy load should be suspended by the hook 27. The hook is raised and lowered by a line 28 which may be a single line if light loads are expected or a multipart line as illustrated if heavy loads are expected. The line is wound on and paid out from a winch 29 operated by one or two hydraulic motors 3I acting on the winch, through worm-drive means in some forms.

A typical hydraulic circuit for powering the boom operation is illustrated at the left-hand side of FIG. 5. A pump 36 is driven by a prime mover which, in the case of a shipboard crane, would probably be an electric motor. The pump draws oil from a sump 38. A main control valve 39 has two ports connected respectively to the pump and the sump and also two cylinder" ports connected to opposite ports of the device to be controlled, which in the illustration, is a lift cylinder 23. If there are two such lift cylinders they would be connected in parallel. There are usually auxiliary automatic valves not illustrated. One of the most important is a pilot-actuated valve connected directly at the bottom of cylinders 23, either directly connected to each or connected to pipes as distinguished from hoses, which positively precludes the boom from being lowered unless lowering pressure is applied from valve 39.

Valve 39 is commonly controlled by a handle or lever 41 mechanically coupled by such linkage as is shown, including link 42 to the actuating stem 43 of the valve. As is well known in the art, such stem 43 actuates a spool longitudinally movable within the valve 39. As is widely understood. such a spool has a neutral position at which the oil is either bypassed to the sump or passed to other valves, and may be moved in either direction for either direction of actuation of the controlled member. There is a separate valve such as the valve 39 for each of the four crane functions, swing, telescoping, boom-lift and winch. Of course, there is a separate handle 41 for each valve. Preferably there is separate pumping for each, so that more than one operation at a time can have full power. A bank of such valves is conventionally located within reach of an operators seat 46 which may either be mounted above the turntable to swing with the turntable or below the turntable to be stationary. If it were not to swing, of course there would be an effort to choose a single position of maximum visibility for the expected areas of operation.

REMOTE CONTROL OF PRESENT INVENTION According to the present invention, there need not be any operator in the seat 46. Instead, as shown in FIG. 2, an operator carries a shoulder-mounted control unit 48 connected to the control center in front of seat 46 by a light flexible cable 49. If the operator commonly leans over as much as the draftsman has illustrated in FIG. 2, a stabilizing belt for the unit 48 may be provided, but it is not believed to be necessary. This unit can be quite light in weight.

The units of the remote control system are seen in FIG. 5. The control unit 48 carries a master cylinder 51 for each of the controlled function, thus four of them in the form described. Each of the master units 51 has a handle 52, FIG. 2 showing two visible and two within the operators hands.

As we will see, cylinder 51 operates as a manual pump by which the operator can pump a small quantity of oil out through either port 53 or 54. Each port is connected to a slim tube 56, preferably of nylon which is part of a cable 49 extending from unit 48 to the control center. The two ports of master cylinder 51 are connected to the two ports of a slave cylinder 51' by such tubes, one of the tubes being connected through a pressure reservoir 58. Slave cylinder 51' responds to the small amount of oil pumped by master cylinder 51 to actuate its output lever 61 which is connected by link 62 to link 42 during periods of crane operation by remote control.

When loading of the ship has been completed, spring clip 63 will be removed, pin 64 slipped out, and the entire remote control assembly carried inside to a place protected from the elements. The four slave cylinders 51' and the four pressure reservoirs 58 are carried by frame 66 which slips out of brackets 67 which jointly may be regarded as a shelf.

In an emergency, the crane could be operated by its handles 41 without the delay to restore the remote control apparatus to the shelf and connecting the link 62 to the links 42.

MASTER AND SLAVE CYLINDERS The cylinders 51 and 51' are identical, except for the different levers connected to their spindles 71, and therefore only the master cylinder 51 will be described. The spindle 71 carries a pinion or part-pinion 72 which meshes with teeth on a piston rod 73. The piston rod 73 carries a piston 74 which slides in sealed engagement along the polished inside cylinder wall 76. The piston rod is also sealed in its sliding engagement with a cylinder cap 77 which is conveniently removable from but sealed to the body of cylinder 51, being retained in place by a snap ring 78. O-rings 79 form the sealing means wherever appropriate.

It is apparent that when the handle 52 is actuated to move piston rod 73 and piston 74, oil will be moved and forced out from either port 53 or port 54, to actuate the slave cylinder. Because no slave cylinder 51' is shown in cross section, the actuation at the slave cylinder can best be described by reference to cylinder 51. In fact, if an operator in seat 46 should momentarily take over control of the crane while the remote control apparatus is installed, cylinder 51 becomes the slave cylinder because operation of a handle 41 would move the piston rod 73 of cylinder 51' which now becomes the master cylinder. Thus movement of its piston rod 73 and associated piston will force oil out of one of the ports 53' or 54, and the effect of this oil on cylinder 51 which has now become temporarily the slave cylinder, can be described with reference to FIG. 6.

If it is assumed that the oil forced from cylinder 51' has no place to go except into port53 of cylinder 51. it will move the piston 74 outwardly toward cap 77 the exact amount of the movement of the piston in cylinder 51. Oil from below piston 74 in cylinder 51 will be forced out through port 54 to occupy the space left by the moving piston in the cylinder 51.

It will be observed that the displacement is of the same value on both sides of piston 74, inasmuch as the piston rod 73 extends through the cylinder heads in both directions.

PRESSURED RESERVOIR In order for the handle 52 to have the same feel as the handle 41 and to meet the same responsiveness of the control valve operated by it, it is necessary that no backlash be added by the nature of the remote control system. To avoid such backlash effect, it is desirable that the hydraulic lines be kept under pressure, and substantially free from entrapped air. To this end, a pressured reservoir 58 is provided for each masterslave combination.

As illustrated in FIG. 6, reservoir 58 has two ports 81 and 82 which during normal use are in free communication with one another so that in effect this unit becomes part of one of the lines between the master cylinder 51 and the slave cylinder 52. Both of these ports, however, communicate with a pressure chamber 83 within reservoir 58. One wall of this pressure chamber is movable, being in the form of a piston 84. Piston 84 is carried by a threaded stem or piston rod 86 which screws into the head 87 of pressure reservoir 58. Stem 86 has a handle 88. By taming the handle 88 to advance the piston 84 inwardly, pressure will be applied to the liquid in chamber 83 and to the liquid throughout the remote control system. This pressure need not be great, merely enough so that no initial movement of the piston 74 will be taken up in expanding the connecting lines while the pressure builds up to the point sufficient to actuate slave cylinder 51'.

It is desirable that the hydraulic remote control system be substantially free of air. The pressure reservoir 58 is constructed to facilitate removing the last air from the lines and from the cylinder. If air appears during use, it will tend to be trapped in chamber 83. A very small amount of air in this chamber may be harmless and may even be beneficial in accommodating expansion and contraction of the liquid with changes of temperature. Of course, it maintains a pressure on the hydraulic liquid and hence when above the pressure needed to actuate a valve, normal operation of one piston 74 will actuate the other piston as if there were no air present. If the presence of air becomes noticeable, however, it is merely necessary to unscrew plug 89 to let the air bleed out while handle 88 is turned to advance piston 84 to maintain the pressure. A controlled amount of air will be retained due to the shoulder 91. There has not yet been sufficient testing to determine whether such controlled amount of air is advantageous, disadvantageous or of no consequence whatever. If complete freedom of air proves to be desirable, shoulder 91 will be omitted and there may even be a conical upwardly extending surface to facilitate the upward flow of the last vestige of air.

Bleeding all air from the lines can easily be accomplished with the aid of the reservoir 58. After the lines have all been connected, the piston 84 is backed into engagement with cap 87 and the chamber 83 filled with hydraulic'fluid. Plugs of both cylinders 51 and 51 are unseated to connect openings 90' through a center bore in piston rod 73 to effectuate bypassing of pistons 74(Valve screw 93 of the accumulator may now be turned to move valve plug 94 into position shutting off passage 96. Also, plug 97 is removed. Now handle 88 may be turned to move piston 84 inwardly until air-free hydraulic liquid flows out of port 98 from which plug 97 has been removed. During this operation, each of cylinders 51 and 51' is so positioned that air will not be trapped, or air may be pumped out by moving pistons 74 against both heads, until no more air comes out of port 98.

All air having been bled, plug 97 should be restored to close port 98 and screw 93 is turned to draw valve 94 out and open passage 96.

Handle 88 is then turned to move piston 84 inwardly sufficiently to apply the desired static pressure to the hydraulic fluid to provide the desired degree of tightness. With a static pressure higher than any required to operate valve 39 the slightest movement of handle 52 will be reflected by a corresponding movement of the associated valve stem 43. Most operators may prefer a static pressure just below this, so that there is a softness of an almost imperceptible degree. Pistons 74 are then moved to approximately midpositions, while handle 52 and output lever 61 are both positioned for neutral. Spindle 71 is splined to receive the elements at almost any angle. Finally, plugs 90 are screwed in to close the through-piston bypass.

FURTHER FEATURES A special piston ring for piston 84 is preferred, as shown in FIG. 6. A Teflon slipper seal [01 engages the cylinder wall and it is expanded to seal firmly by an O-ring under considerable radial compression. The Teflon is contracted by a piston ring compressor to insert it into the cylinder and the cylinder is preferably minutely flared at the entry. The Teflon is reliable both in sealing and in having a minimum tendency toward sticking such as would make initial turning of handle 88 difficult after a long time of being stationary.

Care should be taken thatthe hydraulic fluid in the remote control system does not stiffen at colder temperatures to be encountered. The longer the cable, the more important this is. A 40 foot cable has been found satisfactory, but lengths at least to 100 feet are contemplated. A fluid made up of eight parts mineral spirits to one part transmission fluid such as Mobilfluid 200A" has been found satisfactory. For extremely cold temperatures, a heating wire can be run through the cable and around the cylinders 51, 51'. It is hoped however that a modern synthetic constant viscosity fluid will be found satisfactory, the quantity being small enough to make cost per gallon relatively unimportant.

Although control knobs 52 have been shown above the cylinders 51, present preference is to have them below the cylinders so as to be at a more convenient waist-high location. An assembly of cylinders has been provided weighing only 7 pounds. The shoulder-hung rack adds about 4 pounds, but it is so close to the body that its weight is not very significant.

All of the control valves 39 are of the common type that is spring-returned to neutral. Hence, if a hydraulic cable should be severed, all crane functions would stop, a valuable safety feature. Also, an operator feels the increasing spring tension.

If desired, three cylinders 51 can be connected in one series hydraulic circuit. Hence, there can be two remote control units if conditions do not permit one remote control operator to see everything well enough. Likewise, there can be two slave cylinders operated by one master cylinder. in winch control, for example, slow line movement would be achieved by operating the master cylinder enough to open one valve; but the master cylinder could be operated further to operate a second valve for high speed. This second valve may shift two winch motors from parallel to series hydraulic connections or may connect a second pump to the same working circuit. The second valve or its linkage can be designed to require higher pressure from the master cylinder before it opens. Each master cylinder preferably provides full actuation of a single valve with about half its available piston movement, anyway, and so the remaining stroke is available. There is no objection to using it for a nonvital function even though that function might be lost or impaired if the master and slave occasionally creep out of phase due to seepage of fluid past a piston. Tests indicate that such seepage effect will be extremely rare. if it occurs at all.

Some functions, such as operating a second valve for higher speed need not be controlled with manual finesse, and can therefore be operated electrically, by a pair of wires along the hydraulic cable 49 connected to a switch or push button on one of hand levers 52.

The material now preferred for the tubes of cable 49 is nylon. It will be safe for pressures much higher than can be produced manually, without excessive stretching, even at the highest temperatures likely to be encountered. Tubes of about .178 inch ID. and .250 inch O.D. have been found to be satisfactory, using commerciallyavailable cylinders of the type shown as cylinder 51 having an internal diameter of about 1.5 inches, sold by Hydronics Corp.

ACHIEVEMENT With the remote control system of this invention, an operator considerably separated from the control center of a hydraulic crane, and free to walk about, can control all of the hydraulic functions of the crane with the same precision and finesse as with the usual control handles mechanically linked to the control valves. Thus, the remote control operator can achieve all of the preciseness, smoothness, and rapidity of operation for which hydraulic cranes are already noted. He can stand at a position in which he has unimpaired vision of the part of the operation in which the crane is immediately employed, and in most instances he will be able to choose the position such that with only a few steps walk at most, he will also be able to have an unobstructed vision of the remainder of the crane operation. On rare occasions, it may be desirable to have an operator in the crane operator seat, also. This would be particularly true if good vision of one phase of the crane operation required the remote control operator to be at a location from which he would be unable to see the remainder of the crane operation. The two operators could pass control from one to another quite smoothly, inasmuch as each would be able to feel on his handle any thrust applied by the other. For example, the operator at the crane location in lowering a load beyond his range of good vision into the area where he expected the remote operator to take over could start to close the lowering valve. Before this closing movement reached a point of having any effect, the remote control operator would feel it and could signal that he was taking over by pressing his lever back to the full open position. Should either operator see any emergency, he could easily overpower the other operator to close a valve and stop an operation simply by exerting a little greater than normal force. From either position, the valves operate so easily that either operator would always recognize an abnormal force in the closing direction as being an emergency takeover.

In most situations, however, a single operator would be sufficient since he would at all times be able to keep his eyes on the load and know exactly what valve control operation would be appropriate.

An example of great usefulness of this invention other than on shipboard is in connection with construction work. A ground operator can run the crane for picking up a load. An operator on the floor being constructed can take over operation for accurately and gently placing a load, even if it is swaying to an extent making deposit by hand signal too dangerous.

I claim:

1. The combination of:

a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom;

remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, a slave cylinder identical to the master cylinder. having ports at opposite ends directly, constantly. and openly communicating with ports at opposite ends of each corresponding master cylinder and having a piston therein hydraulically coupled to the piston of the master cylinder to reflect its movements. said slave cylinder piston being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder;

the coupling of the master and slave cylinders being through a flexible cable of plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point;

a single-chamber cylinder connected to one hydraulic line for applying static pressure to the hydraulic system to avoid hydraulic backlash, said cylinder having as its sole means for applying the static pressure a screw-actuated plunger; and

manual bypass valve for the master cylinder piston whereby when the application of static pressure by the screw-actuated plunger causes the two pistons to be out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the spring-centered valve it controls.

2. The combination of:

a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom;

remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, a slave cylinder identical to the master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of each corresponding master cylinder and having a piston therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder;

the coupling of the master and slave cylinders being through a flexible cable of plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point;

a single-chamber cylinder connected to one hydraulic line for applying static pressure to the hydraulic system to avoid hydraulic backlash, said cylinder having as its sole means for applying the static pressure a screw-actuated plunger; and

the single-chamber cylinder being connected within a line, between two parts of that line, for flow through this cylinder between the master and slave cylinder for closing its connection to one line part and opening that line part to atmosphere for filling the lines and the slave and master cylinders with hydraulic fluid from the singlechamber cylinder.

3. The combination of:

a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom horizontal swing, rise and extension movements and paying out and drawing in a line extending downwardly from the end of the boom;

remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, slave cylinder means for each master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of the master cylinder and having piston means therein hydraulically coupled to the iston of the master cylinder to reflect its movements, sal slave cylinder piston means being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder;

the coupling of the master cylinders and slave cylinder means being through a flexible cable of slim plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point;

means substantially nonyielding to manually derived hydraulic pressure for applying static pressure to the hydraulic system to avoid hydraulic backlash; and

a manual bypass valve for each master cylinder piston whereby when its piston and the associated slave piston means have become out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the springcentered valve it controls.

4. The combination of:

a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom;

remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, slave cylinder means for each master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of the master cylinder and having piston means therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston means being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder;

the coupling of the master cylinders and slave cylinder means being through a flexible cable of plastic tubes;

means substantially nonyielding to manually derived hydraulic pressure for applying static pressure to the hydraulic system to avoid hydraulic backlash; and

a manual bypass valve for each master cylinder piston whereby when its piston and the associated slave piston means have become out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the springcentered valve it controls. 

1. The combination of: a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom; remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, a slave cylinder identical to the master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of each corresponding master cylinder and having a piston therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder; the coupling of the master and slave cylinders being through a flexible cable of plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point; a single-chamber cylinder connected to one hydraulic line for applying static pressure to the hydraulic system to avoid hydraulic backlash, said cylinder having as its sole means for applying the static pressure a screw-actuated plunger; and a manual bypass valve for the master cylinder piston whereby when the application of static pressure by the screw-actuated plunger causes the two pistons to be out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the spring-centered valve it controls.
 2. The combination of: a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom; remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, a slave cylinder identical to the master cylinder, having ports at opposite ends directly, constantly, and openly communicaTing with ports at opposite ends of each corresponding master cylinder and having a piston therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder; the coupling of the master and slave cylinders being through a flexible cable of plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point; a single-chamber cylinder connected to one hydraulic line for applying static pressure to the hydraulic system to avoid hydraulic backlash, said cylinder having as its sole means for applying the static pressure a screw-actuated plunger; and the single-chamber cylinder being connected within a line, between two parts of that line, for flow through this cylinder between the master and slave cylinder for closing its connection to one line part and opening that line part to atmosphere for filling the lines and the slave and master cylinders with hydraulic fluid from the single-chamber cylinder.
 3. The combination of: a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom horizontal swing, rise and extension movements and paying out and drawing in a line extending downwardly from the end of the boom; remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, slave cylinder means for each master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of the master cylinder and having piston means therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston means being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder; the coupling of the master cylinders and slave cylinder means being through a flexible cable of slim plastic tubes, and the master cylinders being on a frame suitable for mounting on the human body for carrying from point to point; means substantially nonyielding to manually derived hydraulic pressure for applying static pressure to the hydraulic system to avoid hydraulic backlash; and a manual bypass valve for each master cylinder piston whereby when its piston and the associated slave piston means have become out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the spring-centered valve it controls.
 4. The combination of: a hydraulic crane having spring-centered valves controlling hydraulic actuation of crane functions including boom movement and paying out and drawing in a line extending downwardly from the end of the boom; remote control means for actuating the crane-control valves including a master cylinder for each hydraulic crane-control function having its piston position therein responsive to manual control by a control lever, slave cylinder means for each master cylinder, having ports at opposite ends directly, constantly, and openly communicating with ports at opposite ends of the master cylinder and having piston means therein hydraulically coupled to the piston of the master cylinder to reflect its movements, said slave cylinder piston means being mechanically coupled to the corresponding crane-control valve so that the movement of the control element thereof reflects the movement of the control lever of the master cylinder; the coupling of the master cylinders and slave cylinder means being through a flexible cable of plastic tubes; means substantially nonyielding to manually derived hydraulic pressure for applying static pressure to the hydraulic system to avoid hydraulic backlash; and a manual bypass valve for each master cylinder piston whereby when its piston and the associated slave piston means have become out of phase with one another, the master piston may, with its said valve open, be moved to center position; the slave cylinder piston being, under that condition, spring-centered by influence of the spring-centered valve it controls. 